1. Field of the Invention
The present invention relates to a vehicle power generating device and the like, and more particularly, to reducing an amount of fuel consumed by power generation of an internal combustion engine.
2. Description of the Related Art
Conventionally, a vehicle mounts a generator for supplying electric power to various kinds of electric loads and charging a battery. The generator generates electric power by being driven by an internal combustion engine, and hence, when the internal combustion engine is in operation (excluding when fuel is cut off), the fuel is consumed also by the power generation.
In view of this, vehicle fuel efficiency improvement has been demanded in recent years to deal with environmental matters. There have been proposed a method of actively performing power generation when the internal combustion engine cuts off the fuel, such as when the vehicle is decelerating (hereinafter referred to as power regeneration), to thereby reduce the chance for the internal combustion engine to perform power generation involving fuel consumption (hereinafter referred to as combustion power generation), and a method of setting the operating region of the internal combustion engine as the condition for performing combustion power generation, to thereby reduce the amount of fuel consumed by power generation (see, for example, Japanese Patent No. 4158615). In the conventional technology, based on a fuel consumption map in which incremental power of the internal combustion engine obtained by power generation is added, power generation is performed in an operating region of the internal combustion engine, where fuel consumption is small, to thereby reduce the amount of fuel consumed by power generation.
The conventional technology disclosed in Japanese Patent No. 4158615, however, takes no consideration of a charged state of the battery during power generation. In particular, in the case of a generally-used lead-acid battery, the charge acceptance tends to deteriorate as the state-of-charge (hereinafter referred to as SOC) of the battery becomes higher. Thus, when the SOC of the battery becomes higher than necessary because of excessive combustion power generation, the charge acceptance in power regeneration deteriorates to reduce regenerated energy. The reduced regenerated energy is compensated for by increasing the chance of combustion power generation. As a result, there has been a problem of the increased amount of fuel consumed by power generation.